rbufexample: Using resizable buffer descriptors

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Click on the following link to download the example: rbufexample.zip .

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Description

• Creating an RBuf

• Swapping two RBufs

• Copying data to an RBuf using the assignment operator

• Reallocating an RBuf

• Replacing and modifying the data in an RBuf

Creating an RBuf

The example demonstrates creating an RBuf in the following ways:

1. Using RBuf::Create() or RBuf::CreateL(): These functions create either an empty descriptor, or one with data copied from another descriptor.

2. Using RBuf::CreateMax() or RBuf::CreateMaxL(): These functions set the buffer's current length to be the same as its maximum length.

3. By assigning from an HBufC: RBuf::Assign(HBufC8*) transfers ownership of the heap descriptor. It is not possible to access the original heap descriptor once ownership has been transferred.

4. By assigning some previously allocated memory: RBuf::Assign(const RBuf8& ) transfers ownership of allocated memory. It is then not possible to access the original memory.

5. Using RReadStream: The example writes some text to a file stream ( RFileWriteStream ). Then it creates the buffer by passing the open stream object to RBuf::CreateL(TInt) .

Related APIs

• RBuf - Defines a build-independent resizable buffer descriptor.

• RBuf::Assign(const RBuf8&)

• RBuf::Create(const TDesC8&)

• RBuf::CreateL(const TDesC8&)

• RBuf::CreateMax(TInt)

• RBuf::CreateMaxL(TInt)

Swapping two RBufs

The example creates two resizable buffers using RBuf::Create(const TDesC8&) . Then it swaps the contents of them using RBuf::Swap(RBuf8&) .

Note: When you swap data between two RBuf s ensure that the maximum length of the target RBuf is sufficient to hold the data, otherwise a panic ( User 11 ) occurs.

Related APIs

• RBuf::Create(const TDesC8&)

• RBuf::Swap(RBuf8&)

Copying data to an RBuf using the assignment operator

The example creates two resizable buffers and allocates memory using RBuf::Create(const TDesC8&) . It then copies data to these buffers. It also copies data from the first buffer to the second buffer using the assignment operator.

Notes:

• When you use RBuf::Assign(const RBuf8&) , ownership of the buffer is transferred. Assign(const RBuf8&) neither checks nor frees any pre-existing owned allocated memory. If this descriptor already owns some allocated memory, RBuf16::Close() should be invoked on it before calling RBuf::Assign(const RBuf8&) , otherwise a memory leak will occur.

• When you use the assignment operator, you must make sure the target descriptor's maximum length is equal to or greater than the length of the source descriptor, otherwise a User 11 panic (descriptor overflow) occurs. Any existing data in the target descriptor is replaced.

Related APIs

• RBuf16::Close()

• RBuf::Assign(const RBuf8&)

• RBuf::Create(TInt)

Reallocating an RBuf

The example creates a resizable buffer descriptor, then it resizes it using RBuf::ReAlloc(TInt) . The old and new lengths are printed to the console to show how ReAlloc() does not change the length of the descriptor, but only its maximum length. Calling RBuf::ReAlloc(TInt) with a value of zero frees the memory and sets the length and maximum length to zero.

Related APIs

• RBuf::ReAlloc(TInt)

Replacing and modifying the data in an RBuf

The example creates a resizable buffer descriptor and replaces a portion of the data in it using RBuf::Replace(TInt ,TInt ,const TDesC16&) . The start position and length of the data to be replaced, and the replacement text are passed as parameters. RBuf::Delete(TInt , TInt) is then used to delete the replacement text, by specifying the position and length of the data to be deleted.

Related APIs

• RBuf::Delete(TInt , TInt)

• RBuf::Replace(TInt ,TInt ,const TDesC16&)

Class summary

• RBuf - Defines a build-independent resizable buffer descriptor.

• HBufC - Defines a build-independent heap descriptor.

• RFileWriteStream - Supports the writing of a stream to a file.

• RFileReadStream - Supports the reading of a stream from a file.

• RFs

Build

The example builds an executable file called rbufexample.exe in the standard location ( \epoc32\release\winscw\<build_variant> for the emulator). After launching the executable, depending on the emulator you are using, you may need to navigate away from the application launcher/shell screen to view the console.

See also

How to use the resizable buffer descriptor - RBuf